GE Power Systems

GE Combined-Cycle

Product Line and

Performance

D.L. Chase

P.T. Kehoe

GE Power Systems

Schenectady, NY

GER-3574G g

Contents

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

STAG Product Line Designations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

STAG Product Line Configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

STAG Power Generation Product Line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

STAG Combined-Cycle Major Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Gas Turbines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

HRSG. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Steam Turbine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Generators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Auxiliaries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Plant Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Plant Arrangements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Installation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Utility Load Growth. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Thermal Energy and Power System Product Line. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Engineered Equipment Package. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

GE Combined-Cycle Product Line and Performance

GE Power Systems ■ GER-3574G ■ (10/00) i
GE Combined-Cycle Product Line and Performance

GE Power Systems ■ GER-3574G ■ (10/00) ii
Introduction

The development during the past four decades

of larger capacity gas turbine designs (50 MW to

380 MW) with increased specific power has led

to the parallel development of highly-efficient

and economical combined-cycle systems. The

GE pre-engineered, combined cycle product

line is designated STAGTM, which is an acronym

for STeam And Gas. Each STAG combined

cycle system is an Engineered Equipment

Package (EEP) consisting of GE gas turbines,

steam turbines, generators, Heat Recovery

Steam Generators (HRSGs) and controls. The

most efficient of these STAG systems is configured with the GE "H" model gas turbine and is

scheduled for commercial operation by the year

2003. The “H” combined cycle will achieve 60

percent (LHV) thermal efficiency.

The STAG EEP is an optimized and matched

system of high technology power generation

equipment, software, and services configured

for convenient integration with the owner's auxiliaries and balance of plant equipment to form

an economical power plant. This single source

supply of the EEP enables GE to provide guarantees of plant thermal and emission performance as well as warrant system operation.

The product line spans a wide range of capabilities for both 50 and 60 Hz applications. A wide

range of configurations is available with standard options that enable the systems to be

adapted to suit the economic requirements of

each application. The STAG combined-cycle

product line includes two major categories:

■ Pre-engineered oil- or natural gas-fired

systems for electric power generation

■ Pre-engineered building blocks for

combined-cycle cogeneration systems

and coal- or oil-fired integrated

gasification combined-cycle (IGCC)

power generation systems.

Economical performance of function is the outstanding characteristic of STAG combined-cycle

systems. The features that contribute to economical power generation by STAG combinedcycle power generation systems are shown in

Table 1 and those for thermal and power systems

are presented in Table 2.

STAG Product Line Designations

System designations that identify STAG combined-cycle product line configurations are

defined in Table 3. This example defines the

designation for the single-shaft and multi-shaft

combined-cycle configurations.

GE Combined-Cycle Product Line and Performance

GE Power Systems ■ GER-3574G ■ (10/00) 1

Table 1. STAG combined-cycle power generation

system features

Table 2. STAG combined-cycle thermal energy

and power system features

• High Thermal Efficiency

• Low Installed Cost

• Fuel Flexibility – Wide Range of Gas and

Liquid Fuels

• Low Operation and Maintenance Cost

• Operating Flexibility – Base, Mid-range,

Daily Start

• High Reliability

• High Availability

• Short Installation Time

• High Efficiency in Small Capacity

Increments

• High Thermal Efficiency

• Low Installed Cost

• Low Operation and Mainteance Costs

- Steam Generation at Process Conditions

- Extraction/Condensing Steam Turbine

- Non-Condensing Turbine Exhausting to Process

- Unfired/Fired HRSGs

- Gas Turbine DLN/Steam Injection

• High Power to Thermal Energy Ratio

• High Reliability/Availability

• Short Installation Time 
STAG Product Line Configurations

The product line includes single-shaft and

multi--shaft configurations. Simplified block

diagrams of these configurations are presented

in Figure 1. The single-shaft STAG system consists of one gas turbine, one steam turbine, one

generator, and one HRSG with the gas turbine

and steam turbine coupled to the single generator in a tandem arrangement on a single shaft.

Multi-shaft STAG systems have one or more gas

turbine generators and HRSGs that supply

steam through a common header to a separate,

single steam turbine generator.

Single- and multiple-pressure non-reheat steam

cycles are applied to STAG systems equipped

with GE gas turbines that have rating point

exhaust gas temperatures of approximately

1000°F / 538°C or less. Selection of a single- or

multiple-pressure steam cycle for a specific

application is determined by economic evaluaGE Combined-Cycle Product Line and Performance

GE Power Systems ■ GER-3574G ■ (10/00) 2

GEN GT HRSG

GEN GT HRSG ST GEN

HRSG

GT ST GEN

 S 2 0 7FA - MS

STAGTM Two GT Model Multi-Shaft 

 GTs Series Configuration

 S 1 0 7FA - SS

STAGTM One GT Model Single-Shaft

 GT Series Configuration

STAG IS A REGISTERED TRADEMARK OF GENERAL ELECTRIC(USA)

AND IS AN ACRONYM FOR STeam And Gas

S107FA-SS

S207FA-MS

Table 3. STAG combined-cycle system designations

GT19939

Figure 1. STAG system configurations
tion, which considers plant-installed cost, fuel

cost and quality, plant-duty cycle, and operating

and maintenance cost.

Multiple-pressure reheat steam cycles are

applied to STAG systems with GE gas turbines

that have rating point exhaust gas temperatures

of approximately 1100°F / 593°C or greater.

A generalized combined-cycle, electric power

generation and thermal energy capability map

is presented in Figure 2. This map is typical of a

system supplying process steam at 150 psig/11.4

bars and utilizing a gas turbine with 100 MW

rated output.

The vertical axis of Figure 2 with zero thermal

energy shows the power and thermal efficiency

of combined cycles with unfired, supplementary-fired, and fully-fired steam cycles. The most

efficient power generation cycles are those with

unfired HRSGs having modular pre-engineered

components. These unfired steam cycles are

also the lowest in cost and are, therefore,

applied in the STAG combined-cycle power

generation product line. Supplementary-fired

combined-cycle systems are provided for customer specific applications in which the need

for increased power offsets the corresponding

reduction in thermal efficiency.

The most efficient cycles for cogeneration

applications are those with fully-fired HRSGs, as

indicated by Figure 2, at maximum thermal

energy output. The fully-fired HRSGs are high

in cost because of their water wall construction

and need for field erection. Also, fully-fired

HRSGs may add to emission considerations as

plant siting requirements are evaluated. The

primary regions of interest for cogeneration,

combined-cycle systems are those with unfired

and supplementary-fired steam cycles. These

systems provide a wide range of thermal energy

to electric power ratio, 0–12,000 Btu thermal

energy per kW (0–12,660 kJ per kW), and represent the range of thermal energy capability

and power generation covered by the product

line for cogeneration capability.

STAG Power Generation Product Line

The STAG power generation product line

includes an array of steam cycle options, which

GE Combined-Cycle Product Line and Performance

GE Power Systems ■ GER-3574G ■ (10/00) 3

GT21520B

Figure 2. Generalized combined-cycle performance capability
satisfies a wide range of fuels, fuel cost, duty

cycle, and other economic considerations. This

enables selection of a steam cycle for each application that suits specific economic and operational requirements. Steam cycles utilized in the

STAG product line include:

■ Single-Pressure, Non-Reheat Heat

Recovery Feedwater Heating. This

steam cycle, shown in Figure 3, has an

unfired HRSG with finned tube

superheater, evaporator, and

economizer sections. Energy is

recovered from the exhaust gas by

convective heat transfer. The HRSG

schematic diagram is shown in Figure

4. This is the simplest steam cycle that

can be applied in a combined cycle

and it has been used extensively. It

results in a low installed cost.

Although it does not produce the

highest combined-cycle thermal

efficiency, it is a sound economic

GE Combined-Cycle Product Line and Performance

GE Power Systems ■ GER-3574G ■ (10/00) 4

GT16402A

Figure 3. Single-pressure non-reheat cycle diagram

GT1640B

Figure 4. Single-pressure non-reheat HRSG diagram
selection when fuel is inexpensive,

when applied in peaking type service,

or when burning ash-bearing fuel with

high sulfur content. This steam cycle

is utilized in the STAG product line

primarily with GE gas turbines having

a baseload exhaust gas temperature of

approximately 1000°F / 538°C or less.

The HRSG stack gas temperature with

this steam cycle is approximately 

340°F / 171°C.

■ Multiple-Pressure, Non-Reheat Heat

Recovery / Feedwater Heating. Multipressure steam generation is used to

maximize energy recovery from gas

turbine exhaust. HRSG gas-side and

steam-side temperature profiles for

single- and multiple-pressure steam

cycles are presented in Figures 5 and 6.

This illustrates that increasing the

number of steam pressure levels

reduces the exhaust gas and

steam/water energy difference. Twoor three-pressure steam cycles achieve

better efficiency than the singlepressure systems, but their installed

cost is higher. They are the economic

choice when fuel is expensive or if the

duty cycle requires a high load factor.

The three-pressure steam cycle is

shown in Figure 7 and the HRSG

schematic diagram is shown in Figure

8. This cycle is similar to the singlepressure cycle with the addition of the

low-pressure and intermediatepressure sections. Improved plant

performance with multiple-pressure

steam cycles results from additional

heat transfer surface installed in the

HRSG. The HRSG stack gas temperature is in the range of 

200°F / 93°C to 260°F / 127°C.

■ Three-Pressure, Reheat Heat Recovery

Feedwater Heating. The reheat steam

cycle matches the characteristics of the

“EC,” “F,” and “H” technology gas

turbines. The higher exhaust gas

temperature of 1100°F / 593°C or

greater provides sufficient high

temperature energy to the HRSG to

make the reheat steam cycle practical.

Fuel gas heating to approximately

GE Combined-Cycle Product Line and Performance

GE Power Systems ■ GER-3574G ■ (10/00) 5 Temperature

Heat Transfer

Evaporator Economizer Super

Heater

Pinch

Sub-cool

Approach

Typical Exhaust Gas Temperature

Profile - One Pressure System

Figure 5. Typical exhaust gas/steam cycle temperature profile for single-pressure system
GE Combined-Cycle Product Line and Performance

GE Power Systems ■ GER-3574G ■ (10/00) 6

Heat Transfer

Temperature - °C

HPS

RH

HPS

HPB

IPS

HPE

LPS

IPB

IPE

HPE

LPB

 LPE

Gas Turbine Exhaust Gas

Low Pressure

High Pressure

Intermediate & 

Reheat Pressure

Figure 6. Typical exhaust gas/steam cycle temperature profile for three-pressure system

Bypass

Diverter

Damper HRSG

Fuel

GT Gen ST Gen

Deaerating Cond.

Cond.

Pump

Legend

Steam

Water

Air, Gas

Fuel

Figure 7. Three-pressure non-reheat cycle diagram

GT16405C

Figure 8. Three-pressure non-reheat HRSG diagram
365°F / 185°C, using water supplied

from the HRSG IP economizer

discharge, is also included with the

“EC” and “F” technology gas turbines.

This steam cycle is shown in Figure 9.

The HRSG schematic is presented in

Figure 10.

The “H” platform gas turbines, configured with

hot gas path components cooled with both a

closed-loop, steam-cooling system and an openloop, air-cooling system design, are designated

as MS7001H and MS9001H. The reheat steam

cycle utilized with these gas turbines is closely

integrated with the gas turbine steam-cooling

system. This integration provides additional

incentive to select single-shaft STAG configuration for these gas turbines. The steam cycle

used with the S107H and S109H is shown in

Figure 11. The HRSG schematic is shown in

Figure 12.

These STAG combined-cycle systems are the

most efficient power generation systems currently available. The base configuration for the

STAG power generation combined-cycle product line is designed for high efficiency when firing natural gas or distillate fuel. A summary of

the equipment and system configuration is presented in Table 4.

The 60 Hz STAG power generation product

line ratings are presented in Table 5. Table 6

shows the major equipment in each standard

STAG system. The 50 Hz product line ratings

are presented in Table 7, and Table 8 shows the

major equipment in each of these standard

STAG systems. These ratings are presented for

gas turbine base load operation with natural gas

fuel. Nominal throttle and reheat steam conditions for the non-reheat and reheat STAG product lines are defined in Table 9.

GE Power Systems ■ GER-3574G ■ (10/00) 7

GE Combined-Cycle Product Line and Performance

Figure 9. Three-pressure reheat cycle diagram

Figure 10. Three-pressure reheat HRSG diagram

• Unfired, three-pressure steam cycle

- Non-reheat for rated exhaust gas

temperature less than 1000°F/538°C

- Reheat for rated exhaust gas temperature

higher than 1050°F/566°C and fuel heating

- Heat recovery feedwater heating

- Feedwater deaeration in condenser

- Natural circulation HRSG evaporators

• Gas turbine with Dry Low NOx combustors

• Once-through condenser cooling water system

• Multi-shaft systems

• Single-shaft systems

- Integrated equipment and control system

Table 4. STAG power generation combined-cycle

base configuration
The STAG product line equipment and plant

natural gas fuel ratings defined in Tables 5 and 7

represent thermodynamic optimum performance that is expected to be the economic optimum configuration for baseload and mid-range

dispatch using clean fuels costing about $2.50

per 106 Btu, HHV ($2.64 per 106 Kj, HHV). A

wide array of options is available for the STAG

power generation product line to suit specific

economic criteria as well as the operating and

installation preferences of the owner. Table 10

lists the most commonly-applied options in

addition to the base configuration.

Non-reheat steam cycles with one or two pressures and reheat steam cycles with two pressures

are also available for the STAG product-line systems. Typical performance variation for these

optional steam cycles is presented in Table 11.

HRSGs with forced circulation evaporators are

available to suit specific installation situations

and owner preferences. Figure 13 shows a twopressure, non-reheat steam cycle with forced

circulation HRSG.

Systems can be provided with a deaerator integral to the HRSG that utilizes low-pressure evaporator energy to perform the feedwater deaeration at positive pressure at a small reduction in

thermal efficiency. Those systems that include a

GE Combined-Cycle Product Line and Performance

GE Power Systems ■ GER-3574G ■ (10/00) 8

C oolin g

Water

C o o ling A ir

C ooling

 S ystem

To

Stack

Air

Gas Tu rb in e

Air Tre atment

Cond en sate Pu mp

Fuel

H P IP

H eat Recovery

Steam Generator Fu el

 Heatin g

System

Glan d S eal

Cond en ser

Deaerating

Condenser

LP LP G en erato r

Attemp

Filte r

LEGE ND

Filter

A

Filter

B

F eed water

Pump

C on densate Filter

Fuel

Steam

W ater

Exhaust

Air

Steam Tu rb in e

Figure 11. STAG 107H/S109H cycle diagram

T O H P TU RB IN E

T o

Stack

H e at Re c o v e ry

Steam Generator

Atte mp

LEGEND

Feedw ater

Pump

FR OM C ON D ENSA TE PUM P

Fuel

Steam

Water

Exhaust

Air

TO FUEL HEATING SY STE M

TO COOLING AIR COOLING SYSTEM

FROM COOLING AIR COOLING

SYSTEM

FROM GT E XHAUST

T O IP T UR B IN E

TO LP TU RB IN E

FR OM H P T UR B IN E

EXHAUST

T O G T C OO LIN G

Figure 12. HRSG schematic for S107H/S109H
low-pressure economizer for high thermal efficiency will require material that resists corrosion because feedwater passing through this section may have a high oxygen concentration,

and the external tube surface temperature may

be below the exhaust gas dew point temperature. Figure 14 shows a three-pressure nonreheat HRSG with integral deaerator.

Fuel characteristics affect combined-cycle performance in a variety of ways. High hydrogen

content in fuels such as natural gas results in

high water content in the combustion products.

Water has a higher heat content than air or other

combustion products, so fuels with high hydrogen content increase output and efficiency. Ashbearing fuels foul the gas turbine and HRSG;

therefore, equipment and system design considerations that accept fouling reduce plant output

and efficiency. Sulfur content in the fuel may

require adjustment in the temperature of the

stack gas and the water entering the HRSG economizer to prevent condensation of corrosive sulGE Combined-Cycle Product Line and Performance

GE Power Systems ■ GER-3574G ■ (10/00) 9

Combined cycle Net Plant Net Plant Heat Rate(LHV) Thermal

Designation Power (MW) Btu/ kWhr kJ/ kWhr Efficiency (%, LHV) 

S106B (4) 64.3 6960 7340 49.0

S206B (4) 130.7 6850 7230 49.8

S406B (4) 261.3 6850 7230 49.8

S106FA (5) 107.1 6440 6795 53.0

S206FA (5) 217.0 6355 6705 53.7

S107EA (4) 130.2 6800 7175 50.2

S207EA (4) 263.6 6700 7070 50.9

S107FA (5) 262.6 6090 6425 56.0

S207FA (5) 529.9 6040 6375 56.5

S107FB (5) 280.3 5950 6280 57.3

S207FB (5) 562.5 5940 6260 57.5

S107H (6) 400.0 5690 6000 60.0

Notes: 1. Site conditions =59 F, 14.7 psia, 60% RH (15 C, 1.013 bar)

2. Steam turbine exhaust pressure = 1.2 inches Hg,A (30.48 mm Hg,A)

3. Performance is net plant with allowance for equipment and plant auxiliaries

 including those associated with a once-through cooling water system

4. Three-pressure, non-reheat, heat-recovery feedwater heating steam cycle

5. Three-pressure, reheat, heat-recovery feedwater heating steam cycle with

 integrated fuel, gas-heating system

6. Three-pressure, reheat, heat-recovery feedwater heating steam cycle with

 integrated turbine steam- and air-cooling and fuel-heating systems

Table 5. 60 Hz STAG product line performance

Thermal

Efficiency (%, LHV)

 Steam Turbine

Gas Turbine HRSG Exhaust LSB Exhaust

Designation No. Frame No. Type No. Inches mm Config.

• Heavy Duty GT

S106B 1 PG6581 B 1 Non-Reheat, Unfired 1 23 584 Axial

S206B 2 PG6581 B 1 Non-Reheat, Unfired 1 33.5 851 Axial

S406B 4 PG6581 B 2 Non-Reheat, Unfired 2 33.5 851 Down

S106FA 1 PG6101 FA 1 Reheat, Unfired 1 30 762 Axial

S206FA 2 PG6101 FA 1 Reheat, Unfired 2 30 762 Down

S107EA 1 PG7121 EA 1 Non-Reheat, Unfired 1 33.5 851 Axial

S207EA 2 PG7121 EA 2 Non-Reheat, Unfired 2 33.5 851 Down

S107FA 1 PG7241 FA 1 Reheat, Unfired 2 30 762 Down

S207FA 2 PG7241 FA 2 Reheat, Unfired 4 30 762 Down

S107FB 1 PG7251 FB 1 Reheat, Unfired 2 30 762 Down

S207FB 2 PG7251 FB 2 Reheat, Unfired 4 30 762 Down

S107H 1 PG7001 H 1 Reheat, Unfired 2 40 1016 Down

Table 6. 60 Hz STAG product line equipment
furic acid. The increased stack gas temperature

required by higher sulfur content decreases output and efficiency. Performance variation with

fuel type (hydrogen, ash and sulfur content typical of each) is presented in Table 12.

The STAG product line includes gas turbines

with Dry Low NOx (DLN) combustors that can

operate with stack gas NOx emission concentration as low as 9 ppmvd at 15% oxygen (15.5

g/GJ) without water or steam injection, when

operating on natural gas fuel. Water or steam

injection may be required to meet NOx emission requirements when operating on distillate

oil fuel. Also, gas turbines are available with

conventional, diffusion flame combustors operating with water or steam injection to meet NOx

emission limits. Table 13 presents stack gas NOx

emissions from gas turbines in typical STAG

combined cycle systems for operation with DLN

or diffusion flame combustors with natural gas

fuel. The effect of water- or steam-injection on

NOx abatement and thermal performance is

also presented.

Selective catalytic reduction (SCR) is a stack gas

NOx reduction system that uses ammonia to

react with NOx over a catalyst that reduces NOx

to nitrogen and water. These systems increase

the plant installation and operating cost, but

GE Combined-Cycle Product Line and Performance

GE Power Systems ■ GER-3574G ■ (10/00) 10

Combined cycle Net Plant Net Plant Heat Rate (LHV) Thermal

Designation Power (MW) Btu/kWhr kJ/kWhr Efficiency (%, LHV)

S106B (4) 64.3 6950 7340 49.0

S206B (4) 130.7 6850 7230 49.8

S406B (5) 261.3 6850 7230 49.8

S106FA (5) 107.4 6420 6775 53.2

S206FA (4) 218.7 6305 6650 54.1

S109E (4) 189.2 6570 6935 52.0

S209E (4) 383.7 6480 6840 52.7

S109EC (5) 259.3 6315 6660 54.0

S209EC (5) 522.6 6270 6615 54.4

S109FA (5) 390.8 6020 6350 56.7

S209FA (5) 786.9 5980 6305 57.1

S109H (6) 480.0 5690 6000 60.0

Notes: 1. Site conditions = 59 F, 14.7 psia, 60% RH (15 C), 1.013 bar)

 2. Steam turbine exhaust pressure = 1.2 Inches HgA (30.48 mm HgA)

 3. Performance is net plant with allowance for equipment and plant auxiliaries including those associated with a once-

 through cooling water system

 4. Three-pressure, non-reheat, heat recovery feedwater heating steam cycle

 5. Three-pressure, reheat, heat-recovery feedwater healing steam cycle with integrated fuel gas heating system

 6. Three-pressure, reheat, heat-recovery feedwater heating steam cycle with integrated turbine steam and air cooling

 and fuel heating systems.

Table 7. 50 Hz STAG product line performance

Steam Turbine

 Gas Turbine HRSG Exhaust LSB Exhaust

Designation No. Frame No. Type No. Inches mm Config.

• Heavy Duty GT

S106B 1 PG6581 B 1 Non-Reheat, Unfired 1 17 432 Axial

S206B 2 PG6581 B 1 Non-Reheat, Unfired 1 33.5 851 Axial

S406B 4 PG6581 B 2 Non-Reheat, Unfired 2 33.5 851 Down

S106FA 1 PG6101 FA 1 Reheat, Unfired 1 26 660 Axial

S206FA 2 PG6101 FA 2 Reheat, Unfired 1 42 1066 Axial

S109E 1 PG9171 E 1 Non-Reheat, Unfired 1 42 1066 Down

S209E 2 PG9171 E 2 Non-Reheat, Unfired 2 42 1066 Down

S109EC 1 PG9231 EC 1 Reheat, Unfired 1 42 1066 Down

S209EC 2 PG9231 EC 2 Reheat, Unfired 2 42 1066 Down

S109FA 1 PG9351 FA 1 Reheat, Unfired 2 33.5 851 Down

S209FA 2 PG9351 FA 2 Reheat, Unfired 4 33.5 851 Down

S109H 1 PG9001 H 1 Reheat, Unfired 2 42 1066 Down

Table 8. 50 Hz STAG product line equipment
they can reduce NOx to less than 9 ppmvd at

15% oxygen (15.5 g/GJ) for all combined-cycle

systems in the product line. The SCR catalyst

typically operates in the 570°F/300°C to

750°F/400°C temperature range, so the catalyst

is typically installed within the high-pressure

evaporator as shown in Figure 15. The ammonia

injection grid is installed upstream of the evaporator where the gas temperature is below the

temperature at which ammonia oxidizes to

form NOx. This provides intimate mixing of the

ammonia and NOx as the gas passes through

the pre-evaporator section.

Carbon monoxide (CO) emissions are low at

gas turbine loads above 50%, typically less than

GE Combined-Cycle Product Line and Performance

GE Power Systems ■ GER-3574G ■ (10/00) 11

Heat Recovery Feedwater

Heater Steam Cycle

Non-Reheat

Three-Pressure

Reheat

Three-Pressure

Steam Turbine Size (MW) ≤ 40 > 40 <60 ≥ 60 > 60

Throttle Pressure (psig) 820 960 1200 1400-1800

(Kg/cm2,g) (58) (68) (84) (98)

Throttle Temperature (°F) 40 Approach to Gas Turbine 1000-1050

(°C) (22) Exhaust Gas Temperature (538-566)

Reheat Pressure (psig) -- -- -- 300-400

(Kg/cm2,g) -- -- -- (21-28)

Reheat Temperature (°F) -- -- -- 1000-1050

(°C) -- -- -- (538-566)

IP Admission Pressure (psig) 100 120 155 300-400

(Kg/cm2,g) (7) (8) (11) (21-28)

IP Admission Temperature (°F) 20 Approach to Exhaust Gas Temperature

(°C) (11) Upstream of Superheater

LP Admission Pressure (psig) 25 25 25 40

(Kg/cm2,g) (1.8) (1.8) (1.8) (2.8)

LP Admission Temperature (°F) 20 Approach to Exhaust Gas Temperature

(°C) (11) Upstream of Superheater

Table 9. STAG product line steam turbine throttle

and admission steam conditions

STEAM CYCLE NOX CONTROL

• Single pressure • Water injection

• Two pressure • Steam injection

• Three pressure* • SCR (NOX and/or CO)

• Reheat • Dry Low NOx combustion*

• Non-reheat CONDENSER

DEAERATION • Water cooled (once-through system)*

• Deaerating condenser* • Water cooled (evaporative cooling tower)

• Deaerator/evaporator integral • Air-cooled condenser

with HRSG FUEL

HRSG DESIGN • Natural gas*

• Natural circulation evaporators* • Distillate oil

• Forced circulation evaporators • Ash bearing oil

• Unfired* • Low BTU coal and oil-derived gas

• Supplementary fired • Multiple fuel systems

* Base configuration

Table 10. Power generation combined-cycle product line system options

STAG 207EA

STEAM CYCLE

NET PLANT

OUTPUT (%)

NET PLANT THERMAL

EFFICIENCY (%)

THREE PRESSURE, REHEAT +0.7 +0.7

THREE PRESSURE, NON-REHEAT BASE BASE

TWO PRESSURE, NON-REHEAT -1.0 -1.0

SINGLE PRESSURE, NON-REHEAT -4.7 -4.7

STAG 107EA

STEAM CYCLE

NET PLANT

OUTPUT (%)

NET PLANT THERMAL

EFFICIENCY (%)

THREE PRESSURE, REHEAT BASE BASE

TWO PRESSURE, REHEAT -1.1 -1.1

THREE PRESSURE, NON-REHEAT -1.2 -1.2

TWO PRESSURE, NON-REHEAT -2.0 -2.0

Table 11. Performance variation with steam cycle
5--25 ppmvd (9-43 g/GJ). Low CO emissions are

the result of highly-efficient combustion.

Catalytic CO emission abatement systems are

also available, if required, for lower emission

rates. The CO catalyst is installed in the exhaust

gas path, typically upstream of the HRSG superheater.

Options such as compressor inlet cooling,

steam or water injection for power augmentation, HRSG supplementary firing and gas turbine peak load capabilities are available for

combined-cycle plant power enhancements.

They are generally applied primarily for peak

period capacity additions.

GE Combined-Cycle Product Line and Performance

GE Power Systems ■ GER-3574G ■ (10/00) 12

Figure 13. Two-pressure non-reheat steam cycle

with forced circulation HRSG

GT21836A

Figure 14. Three-pressure non-reheat HRSG with integral deaerator

STAG 209E

FUEL NET PLANT

OUTPUT (%)

NET PLANT THERMAL

EFFICIENCY (%)

NATURAL GAS BASE BASE

DISTILLATE OIL -3.0 -2.1

RESIDUAL OIL -9.3 -7.6

NOTES 1. OPERATING POINT = BASE LOAD

2. TWO PRESSURE, NON-REHEAT

RECOVERY FEEDWATER

HEATING SYSTEM CYCLE

Table 12. STAG combined-cycle performance variation with fuel characteristics
Compressor inlet cooling that uses evaporative

cooling is an effective means of adding plant

capacity for applications with high ambient air

temperature and low relative humidity. An 85%

effectiveness evaporative cooler is expected to

increase plant output by about 5% during operation at 90°F / 32°C and 30% relative humidity

site conditions.

Evaporative and mechanical chiller systems may

be used to cool gas turbine inlet air to as low as

45°F / 7°C. These inlet cooling systems can

achieve up to 11% capacity increase during

operation at site conditions of 90°F / 32°C and

30% relative humidity. Evaporative cooling and

chilling systems do not improve combined-cycle

plant efficiency; however, they may provide economic peak power addition during warm summer periods.

Supplementary firing of the HRSG can be utilized to increase steam turbine capability by as

much as 100%. This will increase plant capacity

by about 25%. Cogeneration of power and

GE Combined-Cycle Product Line and Performance

GE Power Systems ■ GER-3574G ■ (10/00) 13

Gas Turbine MS7001EA MS7001FA

Combustion

System DLN Diffusion Flame DLN Diffusion Flame

NOx PMVD at

15% O2 (g/GJ)

9

(15.5)

160

(275)

42

(72)

25

(43)

9

(15.5)

212

(365)

42

(72)

Diluent Injection

Water/Fuel by

Wt

0 0 0.81 - 1.04 - 0 0 0.89 -

Steam/Fuel by

Wt

0 0 - 1.22 - 1.58 0 0 - 1.62

STAG Plant

Performance

Net Power (∆%) Base Base +3.5 +1.0 +5.0 +1.1 Base Base +5.4 +2.8

Net Heat Rate

(∆%)

Base Base +3.6 +2.1 +5.2 +3.4 Base Base +3.9 +3.1

Steam Cycle Non-Reheat, Three Pressure Reheat, Three Pressure

Notes: 1. Site Conditions 59°F, 14.7 psia, 60% RH

(15°C, 1.013 bars)

2. Fuel – Natural Gas

Table 13. Effect of NOx control on combined-cycle performance

GT122107B

Figure 15. Three-pressure reheat HRSG with SCR
process energy is usually the incentive for

HRSG supplementary firing; however, peaking

capacity credits, or leveling fuel consumption

over the ambient temperature range to accommodate “take-or-pay” fuel contracts may also justify this option. The incremental efficiency for

power produced by supplemental firing is in

the 34–36% range based on the lower heating

value of the fuel.

While gas turbine water or steam injection can

be applied to enhance plant output as well as

reduce NOx emissions, plant efficiency is

degraded.

Gas turbine peak load capability is available

with many gas turbine configurations and can

add 3–10% combined-cycle plant capacity. This

may be the most economic approach to small

capacity additions for short periods of time

because peak load operation significantly

impacts gas turbine parts life and maintenance

cost. Table 14 summarizes the performance

impact of these combined-cycle power enhancement options.

Combined-cycle systems can be integrated with

gasification systems to form efficient coal- or oilfired power plants with outstanding environmental performance. The standard modules in

the STAG combined-cycle product line can be

readily adapted to integrated gasification combined cycles (IGCCs).

Figure 16 shows a diagram of an advanced technology “H” platform combined-cycle IGCC system with oxygen-blown gasifier and integration

of the air separation unit with the gas turbine.

This advanced technology IGCC system promises to be an economical power generation system that can fire coal, petroleum coke, heavy

residual oil and other solid or low-grade liquid

fuels. The range of ratings for the advanced

technology IGCC plants is as follows:

Net LHV

IGCC Capacity Thermal Eff.

Unit Frequency (Hz) Range (MW) Range (LHV)

STAG 107H 60 400-460 49-51 %

STAG 109H 50 480-550 49-51%

The capacities and efficiencies are shown as

ranges because they vary with the type of gasifiers, gas clean-up systems, air and steam cycle

integration, coal or other fuel analysis, and fuel

moisture content.

GE Combined-Cycle Product Line and Performance

GE Power Systems ■ GER-3574G ■ (10/00) 14

Typical Performance Impact

Power Enhancement Option ∆ Output ∆ Heat Rate

Base Configuration Base Base

Evaporative Cooling GT Inlet Air (85%

Effective Cooler)

+5.2% -

Chill GT Inlet Air to 45°F +10.7% +1.6%

GT Peak Load +5.2% -1.0%

GT Steam Injection (5% of GT Air Flow) +3.4% +4.2%

GT Water Injection (2.9% of GT Air Flow) +5.9% +4.8%

HRSG Supplementary Firing +28% +9%

Notes: 1. Site Conditions = 90°F, 30% RH

2. Fuel = Natural Gas

3. Three Pressure, Reheat Steam Cycle

Table 14. STAG system power enhancement options
STAG Combined-Cycle Major

Equipment

The major equipment for STAG combinedcycle electric power generation systems includes

the line of packaged gas turbine power generation units, unfired HRSGs, steam turbine-generators, and controls. This is a line of proven,

reliable equipment with excellent performance

characteristics for combined-cycle systems. This

equipment includes gas turbine generators and

steam turbine generators manufactured by GE

as well as HRSGs and controls selected to form

a coordinated combined-cycle system for each

application. Features of the major equipment

that are significant for efficient, reliable combined-cycle systems are presented in the following discussion.

Gas Turbines

The ratings of GE gas turbines applied in the

STAG combined-cycle product line are presented in Table 15. Figure 17 shows a cross-section of

the PG7121EA gas turbine typical of GE gas turbines with 2035°F / 1113°C firing temperature.

The PG9171E gas turbine firing temperature is

2055°F / 1124°C. A cross-section of the PG9351

FA gas turbine is shown in Figure 18, which is

typical of the GE gas turbines with 2420°F /

1327°C firing temperature, including the

PG7241FA.

The next generation “FB” and “H” platform gas

turbines are expected to be in commercial service in the first half of this decade. The cross-section of the “H” gas turbine is shown in Figure 19.

This new machine features closed-loop steam

cooling for the first and second stages of its

four-stage turbine. In order to optimize performance at the 2600°F / 1426°C firing temperature, a higher-pressure ratio compressor

derived from the GE CF680C2 aircraft engine

is utilized.

These gas turbines have the following features

that uniquely suit them for combined-cycle

applications:

■ The key performance characteristic of

the gas turbine that influences

combined-cycle performance is

specific power. Specific power is the

power produced by the gas turbine

per unit of airflow (kW output per

lb/sec of compressor airflow).

Combined-cycle thermal efficiency

GE Combined-Cycle Product Line and Performance

GE Power Systems ■ GER-3574G ■ (10/00) 15

GT25099

Figure 16. Advanced technology IGCC system
increases as gas turbine specific power

increases, as shown in Figure 20. This

figure shows that gas turbine firing

temperature is the primary

determinant of specific power.

Improvements in combined-cycle

thermal efficiency have developed

primarily through the increases in gas

GE Combined-Cycle Product Line and Performance

GE Power Systems ■ GER-3574G ■ (10/00) 16

Heavy-Duty Output (kW) Frequency (Hz)

PG6581 B 42,100 50 and 60

PG6101 FA 70,140 50 and 60

PG7121 EA 85,400 60

PG7241 FA 171,700 60

PG9171 E 123,400 50

PG9231 EC 169,000 50

PG7251 FB 184,400 60

PG9351 FA 255,600 60

MS7001 H * 60

MS9001 H * 50

Notes: 1. Fuel = Natural Gas

2. Site Conditions = ISO Ambient

3. Operating Mode = Base Load, Simple Cycle

*Single-Shaft STAG Combined Cycle Configuration Only

Table 15. GE gas turbines applied to STAG product line

Figure 18. MS9001FA heavy-duty gas turbine

Figure 17. MS7001EA heavy-duty gas turbine
turbine firing temperature, which have

resulted from the development of

high-temperature / high strength

materials, corrosion-resistant coatings,

and improved cooling technology.

Commercial development of

combined cycles and improvements in

combined-cycle efficiency have

proceeded in parallel with advances in

gas turbine technology.

■ STAG systems that utilize the “F”

technology gas turbines achieve net

thermal efficiencies of 53% (LHV) or

greater. STAG systems that utilize “H”

technology gas turbines achieve net

thermal efficiencies of 58–60% (LHV).

These gas turbines have a rated firing

temperature of 2420°F / 1327°C and

2600°F / 1426°C, respectively. The

“FA” technology turbine has a 15.5

pressure ratio, whereas the “H”

technology turbine has a 23.0 pressure

ratio. These designs provide the

highest gas turbine specific power for

this firing temperature. High specific

power provides the lowest simple-cycle

installed cost in addition to high

combined-cycle efficiency.

■ The exhaust gas temperature range of

1000–1100°F / 538–566°C is uniquely

suited to efficient combined cycles

because it enables the transfer of heat

from exhaust gas to the steam cycle to

take place over a minimal temperature

difference. This temperature range

results in the maximum in

thermodynamic availability while

operating with highest temperature

and highest efficiency steam cycles.

■ Multiple can-annular type combustors

with film and impingement cooling

meet the environmental requirements

for applications throughout the world.

They provide reliable operation at

high firing temperatures while

burning fuels that range from natural

gas to residual oil. 

■ Turbine materials, coatings and

cooling systems enable reliable

operation at high firing temperatures.

This achieves high gas turbine specific

power and high efficiency for

combined-cycle systems.

GE Combined-Cycle Product Line and Performance

GE Power Systems ■ GER-3574G ■ (10/00) 17

Features

• Closed Loop Steam Cooling

• 4-Stage Turbine

• Compressor Scaled From Proven Design

• Dry Low Nox Combustor GT25129

Figure 19. “H” gas turbine cross-section
■ Most GE current product line gas

turbines are configured with openloop cooling of the turbine hot gas

path. Hot gas path components are in

large part cooled by film cooling that

uses air supplied from the compressor.

This results in a significant exhaust gas

steam temperature drop across the

first stage nozzle, and requires

significant “chargeable air” to cool the

turbine stages. The temperature

drop across the first stage nozzle and

the chargeable cooling losses increase

as turbine inlet temperature increases.

■ The advanced “H” platform gas

turbine is configured with an

integrated closed-loop steam-cooling

system. The change in strategy to the

closed-loop, steam-cooled system

without film cooling allows higher

turbine inlet temperatures to be

achieved without increasing

combustion temperature. This is

because the temperature drop across

the first stage nozzle is significantly

reduced, as shown in Figure 21. Gas

turbine NOx emissions can then be

maintained at low levels at increased

turbine inlet temperature. Another

important benefit of the integrated

closed-loop, steam-cooling system is

the elimination of “chargeable cooling

air” for the first- and second-stage

rotating and stationary airfoils. This

results in two percentage points

improvement in combined cycle

thermal efficiency.

■ Factory packaging and containerized

shipment of small parts achieve low

installed cost and short installation

time.

■ Reliable operation results from

evolutionary design development that

improves parts and components, a

high-quality manufacturing program

that includes operational factory

testing of the gas turbine and

accessory systems, follow-up service

support by experienced installation

and service personnel, and effective

spare parts support.

■ Low maintenance costs are the result

of the combination of the above

features and a design to allow

convenient access. These include

borescope ports to permit inspection

of key parts and components without

dismantling the equipment.

■ The heavy-duty gas turbine product

line has fuel flexibility provided by

accessory systems, combustion systems,

and turbine components, which

enable utilization of a wide range of

liquid and gaseous fuels. These include

150-400 Btu/scf (6520-16,850 kj/nm3)

gaseous fuels, including those derived

from coal, coke, or heavy petroleum

products, and liquid fuels including

naphtha, light distillates, heavy

distillates, crude oil and residual oil. 

HRSG

HRSGs in the GE STAG product line are

unfired and feature modular construction with

finned-tube heat transfer surface and natural or

forced-circulation evaporators. Figure 22 illustrates a natural circulation HRSG with modular

construction. An installation showing two of

these HRSGs operating with MS7001EA gas turbines is shown in Figure 23. Figure 24 illustrates

the modular-construction, forced-circulation

HRSG, and Figure 25 shows an installation of

GE Combined-Cycle Product Line and Performance

GE Power Systems ■ GER-3574G ■ (81000) 18
this type HRSG in a STAG 107EA system.

Each gas turbine exhausts to an individual

HRSG. For STAG systems with a MS6001B gas

turbine, the standard gas ducting is designed so

that two gas turbines exhaust to a single HRSG.

These STAG systems are also available with one

HRSG per gas turbine. The HRSG and auxiliaries are designed for the specific operating

requirements of the STAG combined cycle system. Design features include:

■ Exhaust gas bypass system to provide

fast startup and shutdown and

flexibility of operation for multi-shaft

STAG systems. Exhaust gas bypass

systems are not used with single-shaft

STAG units.

■ Flexible tube support system to enable

fast startup and load following

capability.

■ Low gas side pressure drop for

optimum gas turbine performance.

■ Large, factory-tested modules that can

be shipped to provide short

GE Combined-Cycle Product Line and Performance

GE Power Systems ■ GER-3574G ■ (10/00) 19

GT25454

Figure 20. Gas turbine performance thermodynamics

GT25134

Figure 21. Impact of stage-one nozzle cooling method
installation time and low construction

cost.

■ Fuel flexibility provided by the ability to

operate reliably and efficiently, using

exhaust gas from gas turbines that burn

fuels ranging from natural gas to

residual oil.

Steam Turbine

GE offers a complete line of steam turbines for

combined-cycle applications. Two or more

steam turbine selections are available for each

STAG product line offering. Steam turbines

with different exhaust annulus areas are available to permit optimization to meet specific

condenser cooling conditions. Steam turbines

with large exhaust annulus areas are more

expensive, but provide increased capability and

may be the most economic selection for applications with low steam turbine exhaust pressure. For applications in which steam turbine

exhaust pressures are high, small exhaust annulus-area steam turbines provide comparable or

higher capability and low cost, and therefore

are the economic choice. Figure 26 illustrates

GE Combined-Cycle Product Line and Performance

GE Power Systems ■ GER-3574G ■ (10/00) 20

GT11717

Figure 22. Natural-circulation HRSG modular construction

Figure 23. Two natural-circulation HRSGs operating with MS7001EA gas turbines
the performance difference for four last-stage

buckets that are available for the STAG 107FA

combined cycle. Steam turbine last-stage bucket lengths for the STAG product line steam turbines range from 14.3 inches / 363 mm to 42

inches / 1067 mm.

Because there are no extractions for feedwater

heating, and steam is generated and admitted

to the turbine at three pressures, the flow at the

exhaust is approximately 30% greater than the

throttle flow. The turbine’s last stage generates

up to 15% of the steam turbine output, so the

efficiency of the turbine's last stage and the sizing of the exhaust annulus area are particularly

important for combined-cycle applications.

As with all modern GE steam turbine last-stage

buckets, the continuously-coupled design is

used for high efficiency and reliability.

Continuously-coupled designs permit the use of

many relatively slender blades with narrow,

GE Combined-Cycle Product Line and Performance

GE Power Systems ■ GER-3574G ■ (10/00) 21

GT00477C

Figure 24. Forced-circulation HRSG modular construction

Figure 25. Forced-circulation HRSG with PG7111EA gas turbines
closely-controlled flow passages, particularly in

the critical high-velocity tip region. Covers

reduce tip leakage losses, provide damping, and

help to maintain control of the flow passage.

Steam turbine designs for high exhaust pressure operation typical of those that are needed

for air-cooled condenser operation at high

ambient temperature are available. These steam

turbine designs are capable of reliable and efficient operation at exhaust pressures up to 15

inches Hg,a/381mm Hg,a.

Advanced 3D aero packages incorporate

advanced vortex design, contoured inlet section

sidewalls, and additional radial tip spill strips for

steam turbines larger than 80 MW, which contribute to maximum combined cycle thermodynamic efficiency.

The STAG combined-cycle product line steam

turbines include axial exhaust and down

exhaust configurations. Axial exhaust is preferred for the single-flow steam turbines, typically applied in the small capacity STAG systems. Figure 27 shows a single-flow axial exhaust

steam turbine.

A line of reheat steam turbines designed specifically for combined-cycle service is available for

STAG systems employing the “EC,” “F,” and “H”

technology gas turbines. The single-shaft STAG

107FA, STAG 109FA and STAG 109H are

designed as integrated machines with a solid

turbine/generator coupling and a single-thrust

bearing that includes common lubrication and

hydraulic and control systems for both gas turbine and steam turbine. A two-flow reheat

steam turbine is shown in Figure 28.

Steam turbines specially designed for combined-cycle service have features that include:

■ Assembled modules that can be

shipped and assembled with a low

profile installation that reduces

installation time and cost. (Building

cost, for indoor installation, also is

reduced with the low profile design.)

■ Access for borescopic inspection of

buckets and nozzles without removal

of the turbine upper casing.

■ Fast startup and load-following

capability provided by minimum shaft

diameter in the vicinity of the first

stage, large fillets between wheels and

rotor, long coupling spans, vertical

flexible plate support near the

centerline with keys for maintenance

of alignment, and off-shell valves with

full-arc steam admission.

■ All main steam, cold reheat and hot

reheat steam pipes connect to the

lower half of the shell. This facilitates

removal of the upper half shell for

maintenance, and eliminates the need

for bolted connections in a high

temperature piping.

■ Sliding pressure operation with the

control valves wide open. A control

stage at the inlet is, therefore, not

GE Combined-Cycle Product Line and Performance

GE Power Systems ■ GER-3574G ■ (10/00) 22

Figure 26. STAG steam turbine last-stage bucket

selection
required.

■ Applications at 1800 psig/124 bar,g

use a single wall construction at the

high-pressure stages as well as the

reheat inlet. With 2400 psig/165 bar,g

applications, a short inner shell

encloses the early high-pressure stages.

This reduces the load on the

horizontal joint bolting and reduces

the thickness of the shell flange.

Generators

Generators for the STAG combined-cycle product line gas turbines and steam turbines are factory assembled and tested. Air-cooled generators are standard for the smaller STAG systems

using PG6581B, PG6101FA and PG7121EA gas

turbines. They may be open-ventilated or totally enclosed water-to-air cooled. If open-ventilated, they are equipped with self-cleaning air filters for desert or other dusty or dirty environments, as shown in Figure 29. Hydrogen-cooled

generators are standard for the single-shaft and

larger multi-shaft STAG systems. The hydrogencooled generators can be cooled by plant-coolGE Combined-Cycle Product Line and Performance

GE Power Systems ■ GER-3574G ■ (10/00) 23

GT24388

Figure 27. Non-reheat, single casing, axial exhaust steam turbine

Figure 28. Two-flow, reheat steam turbine
ing water or by ambient air with water-to-air

heat exchangers. Figure 30 shows a typical packaged hydrogen cooled generator for gas turbine

application.

Controls

The STAG combined-cycle plant has a distributed digital control system with a redundant data

highway. The station operator consoles provide

interactive color graphic displays of the overall

STAG plant, with sufficient detail to enable the

operator to conveniently operate the plant.

The control systems for multi-shaft and singleshaft STAG combined-cycle system fundamentally follow the same principle objectives of simplicity, easy starting, automated operation and

superior load following ability. All main components of the combined-cycle plant have individual control panels and interfaces that relay

information and instructions to and from the

plant operator through data highways to the

operator console. The operator console will

have a detailed graphic display with a high level

of detail that enables convenient and informative interaction with the plant as required.

The single-shaft power train is a simple tandem

arrangement that does not include an exhaust

bypass system and is solidly coupled to one generator with a common overspeed protection

device with less auxiliary equipment. Figures 31

and 32 show block diagrams for multi-shaft and

single-shaft arrangements.

The heat recovery combined cycle is a simple

system with a minimum of control loops, as

shown by the control diagram (Figure 33) for a

single-pressure, multi-shaft STAG system. The

simplicity of this system, coupled with wellestablished, automated operation of system

components, enables effective automation of

GE Combined-Cycle Product Line and Performance

GE Power Systems ■ GER-3574G ■ (10/00) 24

Figure 29. Air-cooled generator with self-cleaning

air filter

Figure 30. Typical packaged hydrogen-cooled generator
the complete power plant. This minimizes the

number of control room operators. Most STAG

systems operate with only one control room

operator and one roving operator.

The multi-shaft STAG control is configured to

enable automated startup and operation after

remote manual starting of plant auxiliaries,

remote manual operation of each major component, or operation of the gas turbine-generator units from local-control compartments. The

control configuration enables maximum availability because the plant can be operated

remotely with no additional control room operators. The equipment protection system is provided within the unit controls, so normal protection is maintained during all modes of operation, including local or remote manual operation.

The single-shaft STAG unit control system is a

microprocessor-based controller that coordinates the operation of the components in each

integrated combined-cycle unit and communicates with the plant control. Because of the simple steam cycle, the tandem coupling of the gas

GE Combined-Cycle Product Line and Performance

GE Power Systems ■ GER-3574G ■ (10/00) 25

Figure 31. Distributed control system for plant with multi-shaft STAG combined cycle

Figure 32. Distributed control system for plant with single-shaft STAG combined cycle
and steam turbines to a single generator, and

the elimination of the HRSG exhaust-gas,

bypass system, the single-shaft STAG combinedcycle control is very simple. Starting, operation,

and shutdown of individual units are automatic.

Single-shaft STAG units are controlled by a local

unit control system that is coupled to the central control room operator's console by a data

highway. One control room operator can operate one or more single-shaft STAG combinedcycle units with this type of control system and

the aid of one local operator.

Auxiliaries

The STAG product line ratings are based on

plants with once-through systems (seawater or

river water) for steam turbine condenser cooling. STAG combined-cycle configurations are

also available for operation with a wide range of

owner-specified auxiliaries, including evaporative cooling towers and air-cooled condensers.

Plant capability and efficiency with these systems is expected to be lower because steam turbine exhaust pressure and cooling system auxiliary power consumption are increased.

Plant Operation

Typical STAG plant performance variation with

ambient air temperature is illustrated by the

heat rate and power-output capability ambienttemperature effect curves in Figure 34. Low heat

rate throughout the ambient-air-temperature

range is typical of these plants. The low heat

rate and increase in output as ambient temperature decreases are achieved by the gas turbine

characteristics and optimum equipment matching.

Gas turbine exhaust flow and temperature vary

with ambient temperature and barometric pressure. Steam production and steam turbine output vary with the exhaust gas flow and temperature supply to the HRSG. Steam turbines are

selected to suit specific application requirements. The steam turbines in the standard systems are sized so that their rated flow matches

the steam production. 

Excellent part-load heat rate is achieved on

multi--shaft systems or multiple single-shaft

units by sequentially loading gas turbines to

meet system requirements (Figure 35). This

curve also shows that the plant can operate efficiently following system load with all gas turbines operating. The heat rate increases only

1% at approximately 80% of rating.

GE Combined-Cycle Product Line and Performance

GE Power Systems ■ GER-3574G ■ (10/00) 26

Figure 33. Multi-shaft STAG control diagram
The modulated, inlet guide vanes (IGV) on the

gas turbine compressor contribute significantly

to the excellent part-load performance. The

inlet guide vanes are modulated to control air

flow in the power plant between the “hash

mark” and the point marked “B.” Varying the

air flow maintains nearly constant gas turbine

firing temperature so that the thermodynamic

quality of the cycle remains essentially constant.

The stack and condenser losses vary almost proportionally with output, so that the heat rate

remains almost constant. At loads below the

hash mark, the gas turbine operates with constant air flow, and firing temperature is reduced

as load is reduced.

Fast starting and loading is characteristic of

STAG combined-cycle generation systems. This

enables them to operate in mid-range, with

daily start peaking service as well as baseload.

Typically, STAG systems can achieve full load

within one hour during a hot start and within

approximately three hours for a cold start.

Multi-shaft STAG systems allow the gas turbines

to start independently of the steam cycle and

provide about 65% of the plant capability within 15–25 minutes, depending on the size of the

gas turbine, for hot, warm, and cold starts, as

illustrated in Figure 36. Single-shaft STAG systems are started and loaded to full capacity in

about the same time period as the multi-shaft

STAG systems. The startup sequence and load

profile for the single-shaft systems differ

because the gas and steam turbines are started

as a single integrated unit and not as two separate units. Single-shaft STAG startup is illustrated in Figure 37.

Plant Arrangements

The STAG combined-cycle equipment can be

adapted to installation requirements demanded

by varying climactic conditions, system configuGE Combined-Cycle Product Line and Performance

GE Power Systems ■ GER-3574G ■ (10/00) 27

Figure 34. Combined-cycle, ambient air temperature effect curve

Figure 35. STAG 200 part-load performance
rations and owner/operator preferences. The

equipment is suitable for outdoor installations,

semi-outdoor installations, or fully-enclosed

installations. Plant arrangements have been

designed for each STAG system.

Plan views of STAG combined-cycle arrangements are shown in Figure 38 (multi-shaft,

S406B), Figure 39 (multi-shaft, S207EA), Figure

40 (single-shaft S109E), Figure 41 (multi-shaft,

S207FA), and Figure 42 (single-shaft, S107FA).

An elevation of the single-shaft S107FA is shown

in Figure 43. Figure 44 shows the S107H and

S109H plan and elevation views. The S107H

provides about 58% increase in combined-cycle

power output with only about 10% increase in

footprint area.

A 220 MW STAG 207E installation is shown in

Figure 45. Figure 46 presents a STAG 109FA combined cycle installation. Figure 47 shows a 4000

MW installation with eight STAG 107F and four

STAG 207FA systems at one site. These

arrangements have indoor turbine-generator

equipment and outdoor HRSGs. Figure 48

shows a plant with two STAG multi-shaft combined-cycle units in an indoor installation. For

outdoor installations, the standard gas turbine

enclosures are weatherproof, and weatherproof

lagging is available for the steam turbines.

Installation

The short installation time and low installation

cost of STAG combined-cycle systems are key

features contributing to economical power generation. This is due to factory packaging of all

major components and containerized shipment

of small parts. In addition to low direct construction cost, the short installation time

reduces interest payments during construction.

The standard factory modules and standardized

designs also reduce plant engineering time and

cost.

The time from order to commercial operation

for pre-engineered, standardized STAG designs

is typically 24 months, not including permitting

time. The multi-shaft STAG systems can be

installed in two phases to reduce the time

between order and initial power production.

The gas turbines contribute 65% of the plant

capacity. Typically, the gas turbine can be

installed in less than 18 months to provide

power generation while the steam system is

being installed. Figure 49 is a typical two-phase

multi-shaft STAG combined-cycle installation

schedule.

Utility Load Growth

Power generation economics can be enhanced

by the installation of generation capacity in

small increments as utility load grows. STAG

combined-cycle plants fit this economical pattern because efficient, low-cost plants are available in small blocks of generating capacity.

Flexibility is also available with the pro-generation approach to capacity addition. Initial natural gas/distillate oil-fired, simple-cycle gas turbine installations can be converted to combined

cycle later, when power demands require capacity increases. Plot plan area for the steam cycle

equipment and transmission line capability are

the main considerations during the initial comGE Combined-Cycle Product Line and Performance

GE Power Systems ■ GER-3574G ■ (10/00) 28

GT08936B

Figure 36. Multi-shaft STAG starting times
GE Combined-Cycle Product Line and Performance

GE Power Systems ■ GER-3574G ■ (10/00) 29

Figure 37. Single-shaft STAG starting times

Figure 38. STAG 406B combined-cycle plan

Figure 39. STAG 207EA combined-cycle plan
GE Combined-Cycle Product Line and Performance

GE Power Systems ■ GER-3574G ■ (10/00) 30

Heat Recovery Generator

Generator

Steam Turbine

Condenser Gas Turbine

Figure 40. STAG 109E combined-cycle plan

Figure 41. STAG 207FA multi-shaft combined-cycle plan

Figure 42. Four-unit STAG 107FA combined-cycle plan
GE Combined-Cycle Product Line and Performance

GE Power Systems ■ GER-3574G ■ (10/00) 31

Figure 43. STAG 107FA single-shaft combined-cycle elevation

GT25050

Figure 44. Single-shaft S107H and S109H plan and elevation

Figure 45. STAG 207E installation
mitment for simple-cycle gas turbines. Future

conversion to coal-derived fuels also is an

option for dealing with the long-range uncertainties of conventional fuel availability and

price.

Thermal Energy and Power System

Product Line

The product line of thermal energy and power

combined-cycle systems (cogeneration and district heating systems) are designed with structured flexibility to provide a wide range of

power and thermal energy capacities to suit varied application requirements. The most commonly supplied systems are:

■ Steam generation at process

conditions with HRSG (no steam

turbine)

- Unfired HRSG

- Supplemental-fired HRSG

■ HRSG and non-condensing steam

turbine exhausting to process

- Unfired, one-pressure HRSG

- Unfired, two-pressure HRSG

- Supplemental-fired, one-pressure HRSG

■ HRSG with extraction/condensing

steam turbine

- Unfired, one-pressure HRSG

- Unfired, two-pressure HRSG

- Supplemental-fired, one-pressure HRSG

The capabilities of the thermal energy and

power systems are unique for each gas turbine

frame size, as well as each set of process steam

conditions for systems with both unfired

process HRSGs and unfired HRSGs that have

non-condensing steam turbines. The systems

GE Combined-Cycle Product Line and Performance

GE Power Systems ■ GER-3574G ■ (10/00) 32

Figure 46. Indoor S109FA installation

Figure 47. 4000 MW multi-shaft STAG installation
with fired HRSGs and condensing steam turbines provide extraordinary flexibility in both

thermal energy and power generation capacity

for each gas turbine frame size.

The performance characteristics include the

net plant power, LHV heat content in fuel consumed, thermal energy in steam to process, and

thermal efficiency and fuel charged to power

(FCP). The thermal efficiency for these systems

is calculated by the following equation:

ηTH = 100 x (Qp + QTE) 

QF

Symbols:

ηTH = Thermal efficiency - LHV (%)

QF = LHV heat content of fuel consumption

(Btu/hr, kJ/hr)

Qp = Net power output (Btu/hr, kJ/hr)

QTE = Thermal energy in process steam 

(Btu/hr, kJ/hr)

The fuel charged to power (FCP) is a useful

parameter for comparing an integrated thermal

energy and power system with separate systems

generating the same power and thermal energy.

For this comparison, the LHV heat content of

fuel that would be consumed by a conventional

fired boiler in producing the same thermal energy is subtracted from the LHV heat consumption

of the integrated thermal energy and power system. The resulting FCP can then be compared

with the heat rate of a separate power generation

facility. This will assess the relative performance

of the integrated thermal energy and power system with separate thermal energy and power

generation systems. FCP is calculated by the following equation:

FCP = 100 x (Q p - [QTE/ηB]) 

p 

Symbols:

FCP = Fuel charged to power = LHV 

GE Combined-Cycle Product Line and Performance

GE Power Systems ■ GER-3574G ■ (10/00) 33

Figure 48. Two 207FA multi-shaft combined-cycle installation

Figure 49. Typical multi-shaft, combined-cycle

project schedule
(Btu/kWH, kJ/hr)

QF = LHV heat content of fuel consumption 

(Btu/hr, kJ/hr)

QTE = Thermal energy in process steam 

(Btu/hr, kJ/hr)

ηB = LHV efficiency of fired boiler producing 

equivalent thermal energy (%)

P = Net electrical output (kW)

Cycle diagrams for thermal energy and power

combined cycle with steam generation at

process conditions is presented in Figure 50.

These systems include generation of steam at

process conditions. Figure 50 shows combinedcycle cogeneration systems that produce

process steam with an unfired or supplementary-fired HRSG. HRSG design for supplementary firing provides the maximum process steam

energy supply. Figure 51 shows combined-cycle

cogeneration systems that are equipped with

non-condensing steam turbines.

Many variations of these systems can be furnished to satisfy specific process plant energy

requirements, including:

■ Single automatic-extraction steam

turbines to efficiently supply steam at

two or three pressures.

■ Multi-pressure HRSGs to supply steam

at multiple-pressure and temperature

conditions. The most flexible thermal

energy and power systems are those

that include extraction condensing

steam turbines. Simplified cycle

diagrams for typical systems with single

automatic extraction are shown in

Figure 52. This system has the capability to operate at lower process steam

demands while using the excess steam

generation to produce power in the

condensing section of the steam

turbine. These systems can be

furnished with double automatic

extraction steam turbines and

multiple-pressure HRSGs to satisfy

specific process steam requirements.

Engineered Equipment Package

The GE Combined-Cycle Engineered Equipment Package (EEP) is a unique combination

of equipment and services. It provides the

owner with a plant performance guarantee and

warranty of operation, and the ability to service

the complete power generation system, as well

as the capability to customize the plant design,

auxiliaries, and structures. This is achieved by

including in the GE scope the major combinedGE Combined-Cycle Product Line and Performance

GE Power Systems ■ GER-3574G ■ (10/00) 34

Figure 50. Cycle diagrams – thermal energy and power combined cycle with steam generation at process

conditions
cycle equipment that requires close coordination for assurance of meeting the performance

and operating objectives. The equipment scope

split between GE and the owner is shown in

Table 16.

The services and software scope split is presented in Table 17. Key elements in the GE EEP

scope are the combined-cycle system design and

the interface definition that enable the owner

,or the owner’s architect-engineer or engineerconstructor, to design the plant to meet project

specific requirements.

GE Combined-Cycle Product Line and Performance

GE Power Systems ■ GER-3574G ■ (10/00) 35

Figure 51. Cycle diagrams – thermal energy and power combined cycle with non-condensing steam turbine

Figure 52. Cycle diagrams – thermal energy and power combined cycle with extraction/condensing steam

turbines
Conclusion

The STAG combined-cycle product line, including power generation systems and thermal

energy and power systems ranging from 60 MW

to 750 MW, are efficient, low-cost systems that

meet the environmental requirements of all

countries. The GE combined cycle EEP provides assurance of satisfying performance and

operating objectives while allowing a customized plant that incorporates the owner's

practices and preferences. The attractive economics, reliability, and operating flexibility of

these systems recommend their consideration

for all power generation applications.

GE Combined-Cycle Product Line and Performance

GE Power Systems ■ GER-3574G ■ (10/00) 36

GENERAL ELECTRIC

• GAS TURBINE(S)

• STEAM TURBINE(S)

• GENERATOR(S)

• HEAT RECOVERY STEAM GENERATOR(S)

• PLANT CONTROLS

OWNER

• MECHANICAL AUXILIARIES

• ELECTRICAL AUXILIARIES

• MAIN ELECTRICAL CONNECTIONS

• BALANCE OF PLANT

– FOUNDATIONS AND STRUCTURES

– SWITCHYARD

– FUEL HANDLING AND STORAGE

– PLANT COOLING SYSTEM

– CONSTRUCTION MATERIALS

– SITE PREPARATION MATERIALS

Table 16. Equipment scope split with engineered

equipment package

General Electric

• Plant performance and environmental guarantee

• Combined cycle system design and warranty

• Balance of plant equipment functional specifications

• Equipment interface drawings

• Steady state and dynamic interface definition

• Equipment operation and maintenance

• Operation and maintenance training

• Construction and operation permit support

• Performance and environmental test support

Owner

• Construction and operation permits

• Plant design

• Plant construction

• Plant start-up, commissioning and operation

• Performance and environmental testing

• Site preparation

• Project administration

Table 17. Services and software split with engineered equipment package
List of Figures

Figure 1. STAG system configurations

Figure 2. Generalized combined-cycle performance capability

Figure 3. Single-pressure non-reheat cycle diagram

Figure 4. Single-pressure non-reheat HRSG diagram

Figure 5. Typical exhaust gas/steam cycle temperature profile for single-pressure system

Figure 6. Typical exhaust gas/steam cycle temperature profile for three-pressure system

Figure 7. Three-pressure non-reheat cycle diagram

Figure 8. Three-pressure non-reheat HRSG diagram

Figure 9. Three-pressure reheat cycle diagram

Figure 10. Three-pressure reheat HRSG diagram

Figure 11. STAG 107H/109H cycle diagram

Figure 12. HRSG schematic for S107H/S109H

Figure 13. Two-pressure non-reheat steam cycle with forced circulation HRSG

Figure 14. Three-pressure non-reheat HRSG with integral dearator

Figure 15. Three-pressure reheat HRSG with SCR

Figure 16. Advanced technology IGCC system

Figure 17. MS7001EA heavy-duty gas turbine

Figure 18. MS9001FA heavy-duty gas turbine

Figure 19. “H” gas turbine cross-section

Figure 20. Gas turbine performance thermodynamics

Figure 21. Impact of stage-one nozzle cooling method

Figure 22. Natural-circulation HRSG modular construction

Figure 23. Two natural-circulation HRSGs operating with MS7001EA gas turbines

Figure 24. Forced-circulation HRSG modular construction

Figure 25. Forced-circulation HRSG with PG7111EA gas turbines

Figure 26. STAG steam turbine last-stage bucket selection

Figure 27. Non-reheat, single casing, axial exhaust steam turbine

Figure 28. Two-flow, reheat steam turbine

Figure 29. Air-cooled generator with self-cleaning air filter

Figure 30. Typical packaged hydrogen-cooled generator

Figure 31. Distributed control system for plant with multi-shaft STAG combined cycle

Figure 32. Distributed control system for plant with single-shaft STAG combined cycle

GE Combined-Cycle Product Line and Performance

GE Power Systems ■ GER-3574G ■ (10/00) 37
Figure 33. Multi-shaft STAG control diagram

Figure 34. Combined-cycle, ambient air temperature effect curve

Figure 35. STAG 200 part-load performance

Figure 36. Multi-shaft STAG starting times

Figure 37. Single-shaft STAG starting times

Figure 38. STAG 406B combined-cycle plan

Figure 39. STAG 207EA combined-cycle plan

Figure 40. STAG 109E combined-cycle plan

Figure 41. STAG 207FA multi-shaft combined-cycle plan

Figure 42. Four-unit STAG 107FA combined-cycle plan

Figure 43. STAG 107FA single-shaft combined-cycle elevation

Figure 44. Single-shaft S107H and S109H plan and elevation

Figure 45. STAG 207E installation

Figure 46. S109FA indoor installation

Figure 47. 4000 MW multi-shaft STAG installation

Figure 48. Two 207FA multi-shaft combined-cycle installation

Figure 49. Typical multi-shaft, combined-cycle project schedule

Figure 50. Cycle diagrams - thermal energy and power combined cycle with steam generation 

at process conditions

Figure 51. Cycle diagrams - thermal energy and power combined cycle with non-condensing 

steam turbine

Figure 52. Cycle diagrams - thermal energy and power combined cycle with extraction/

condensing steam turbines

GE Combined-Cycle Product Line and Performance

GE Power Systems ■ GER-3574G ■ (10/00) 38
List of Tables

Table 1. STAG combined-cycle power generation system features

Table 2. STAG combined-cycle thermal energy and power system features

Table 3. STAG combined-cycle system designations

Table 4. STAG power generation combined-cycle base configuration

Table 5. 60 Hz STAG product line performance

Table 6. 60 Hz STAG product line equipment

Table 7. 50 Hz STAG product line performance

Table 8. 50 Hz product line equipment

Table 9. STAG product line nominal steam turbine throttle and admissions steam conditions

Table 10. Power generation combined-cycle product line system options

Table 11. Performance variation with steam cycle

Table 12. STAG combined-cycle performance with fuel characteristics

Table 13. Effect of NOx control on combined-cycle performance

Table 14. STAG system power enhancement options

Table 15. GE gas turbines applied to STAG product line

Table 16. Equipment scope split with engineered equipment package

Table 17. Services and software scope split with engineered equipment package

GE Combined-Cycle Product Line and Performance

GE Power Systems ■ GER-3574G ■ (10/00) 39
GE Combined-Cycle Product Line and Performance

GE Power Systems ■ GER-3574G ■ (10/00) 40